Gas sensors are sensors that measure gas concentration and composition and play an important role in environmental protection and safety monitoring. The gas sensor is used in gases exposed to various components. Due to the large changes in temperature and humidity at the inspection site, there are a large amount of dust and oil mist, etc., so the working conditions are harsh, and the material of the gas to the sensing element Chemical reactions are generated that attach to the surface of the component and tend to degrade their performance. Therefore, the gas sensor has the following requirements: it can detect the allowable concentration of the alarm gas and other standard values of the gas concentration, can work stably for a long time, has good repeatability, fast response, and has little influence on the coexisting substances.
The wave speed and frequency of the surface of the acoustic wave device will drift as the external environment changes. The gas sensor uses this property to coat a surface of the piezoelectric crystal with a gas sensitive film that selectively adsorbs a gas. When the gas sensor interacts with the gas to be tested (chemical or biological, or physical adsorption) When the film quality and conductivity of the gas sensing film are changed, the surface acoustic wave frequency of the piezoelectric crystal is shifted; the gas concentration is different, and the film quality and the conductivity change degree are different, that is, the surface acoustic wave frequency is caused. The changes are also different. An accurate change in the concentration of the reaction gas can be obtained by measuring the change in the frequency of the surface acoustic wave.
